1. Field of the Invention
The present invention relates to interpenetrating polymer networks wherein one of the components is an acidic polysaccharide or a derivative thereof, a process for their preparation, and their use as biomaterials for biomedical and sanitary applications.
2. Description of Related Art
Hyaluronic acid (HA) is a natural heteropolysaccharide composed of alternate residues of D-glucuronic acid and N-acetyl-D-glucosamine. It is a linear polymer with a molecular weight of between 50,000 and 13,000,000, depending upon the source from which it is obtained and how it is prepared and analyzed. In nature, it is present in pericellular gels, in the fundamental substance of connective tissues in vertebrate organisms, of which it is one of the main components, in the synovial fluid of joints, the vitreous humor, umbilical cord tissues, and in cocks'to combs.
Specific fractions of hyaluronic acid with definite molecular weights are known which do not possess inflammatory activity, and which can therefore be used to facilitate wound healing or to substitute the endobulbar fluids or in therapy for joint pathologies by intra-articular injection, as described in European Patent No. 0 138 572 granted to the present Applicants.
Also known are esters of hyaluronic acid, in which all or part of the carboxy groups of the acid are esterified, and their use in pharmaceuticals and cosmetics, and in biodegradable plastic materials, as described in U.S. Pat. Nos. 4,851,521 and 4,965,353, also granted to the present Applicants.
It is a known fact that the application of hyaluronic acid is able to accelerate healing in patients with bedsores, wounds and burns. Its role in the various stages of wound healing has been described, with the aid of a theoretical model, by Weigel et al. ("A model for the role of hyaluronic acid and fibrin in the early events during the inflammatory response and wound healing," J. Theor. Biol., 119: 219, 1986).
Studies aimed at obtaining products (biomaterials) for medical, sanitary and pharmaceutical applications, composed of hyaluronic acid esters or esters of other polysaccharides used as such or in mixtures with other polymers, have led to the creation of various products. These include tissues such as gauzes of varying density (number of threads per centimeter), of varying dimensions and denier (weight per 9,000 meters of thread), films, membranes, gels, guide channels, etc. Some examples of films appear in two patents granted to the present Applicants, namely U.S. Pat. Nos. 4,851,521 and 4,965,353. The use of such materials is limited by the impossibility of using moulding systems for their construction and use.
An interpenetrating polymer network,. IPN, is an intimate combination of two polymers, both in network form, at least one of which is synthesized or cross-linked in the immediate presence of the other. If one of the two polymers is in network form (crosslinked) and the other is a linear polymer (not crosslinked), a semi-IPN results (L. H. Sperling, Interpenetrating Polymer Networks, CHEMTECH, February, 1988. The term IPN currently covers new materials where the two polymers in the mixture are not necessarily bound together, but the components are physically associated. Clearly, these new materials open up the possibility of giving physical, mechanical and manufacturable properties to easily degradable polymers, creating new materials wherein new biological properties can be coupled with their mechanical properties. Examples of newly-developed IPN and applications thereof have been reported wherein one of the two components is a water-soluble polymer (U.S. Pat. Nos. 4,678,468 and 4,747,953).
IPN comprising a naturally occurring polymer and a synthetic polymer for use in the medical, sanitary, and pharmaceutical areas is, however, novel to the present invention.